Early detection of the existence or absence of the treatment effect: A cumulative meta-analysis.

An unexpected promising effect of low molecular weight heparins (LMWHs) on survival in patients with cancer was observed in early trials in post hoc subgroup analyses but not found in more recent trials. To highlight a possible regression over time toward the lack of the antitumoral effect of LMWHs, we performed a cumulative meta-analysis of survival data from randomized controlled trials (RCTs). Medical databases were searched to identify RCTs comparing, in patients with cancer, LMWHs with placebo or no treatment in patients free of venous thromboembolism (VTE), or to vitamin K antagonists in patients who experienced an acute VTE in overall survival. The cumulative hazard ratio (HR) was estimated after each study inclusion in chronological order. Twenty-three studies (12,970 patients) were included. The cumulative meta-analysis of the earlier trials showed a significant improvement in overall survival with LMWHs. This apparent benefit then gradually regressed over time toward an absence of the effect of LMWHs on survival (HR: 0.98 [95% confidence interval, 0.93; 1.03]). Despite supportive experimental data and early clinical findings, the promising antitumoral effect of LMWHs in patients with cancer gradually vanished over time toward a lack of impact on overall survival. This result suggests 'p-hacking' and selective reporting of the positive results from post hoc subgroup analyses in the early studies.

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